Change to use has_privilege and fix navbar

MediaGoblin will soon be changing User.has_privilege to only accept single arguments which require some template changes to the call. In some parts of the template too I have updated them to use User.has_privilege rather than doing the check itself. 

During testing I found a bug where the dropdown navbar was no longer functioning, this is because of a recent change where div was changed from using a class to using an id. I have fixed that too. 

Let me know if there are any problems.